The cause of the outage is not known, nor was Ms Stone able to give any time indication of when power would be restored.

"We have emergency crews on the way to investigate and safely restore power," she said.

"As soon as we know the cause we will let our customers and the media know."

Some power has been safely restored to 10,000 homes and businesses in and around Double Bay. Crews are still working to get power back to 35,000 customers.

The outages come as Sydney summer temperatures continue to soar, sitting around the low to mid 30s across the greater area.

Supply was interrupted shortly before 11.30am today in more than a dozen suburbs, including Randwick, Bondi, Double Bay, Coogee, Point Piper and Rose Bay.

It comes as temperatures have hit a high of 41 degrees in the west today and 40 in the city.

Rebecca Farr, meteorologist for BOM Sydney says the current heatwave has been caused by a stubborn high pressure system.

Traffic lights have blacked out in the area.

"What we have been seeing is a high pressure system over the Tasman Sea and a trough inland drawing warm air from Northern Australia into the state. This pattern has been very consistent and quite stationary over the past month, so we have been seeing very warm temperatures."

From tonight onwards, the temperatures overnight will drop from 23 degrees to a comfortable 18-19 degrees.

Friday's forecast will almost be 20 degrees cooler for Penrith, hovering around 25 degrees and Sydney is expected to hit 24 degrees.